Wikipedia have given the following definition for Minyan: In Judaism, a minyan is the quorum of ten Jewish adults required for certain religious obligations. In more traditional streams of Judaism, only men 13 and older may constitute a minyan; in more liberal streams women are also counted."
Personally I don't know how much Talmud the editor(s) of this page have learned but it seems to fit the normative idea of what constitutes a minyan.
What is hardly ever taken into consideration is the fact that we have two Talmuds.
Yes, one did last 150 years longer than the other. The prevalence of one learning over the other allowed the Bavli to be redacted, edited, its text refined and its rulings refined and clarified. However lets not throw away the history after all it is still Jewish Learning and Limud Tora.
The masses definitely agree that there must be a minyan (10+) for all public services, historically however, we have not seen this as an absolute requirement. From time to time modifactions have been made in order to keep Jewish Practice alive. When these times arise for us to use these sources we must be very careful that the way of our sages never be cast aside without careful consideration. It should be noted that before any serious decisions are made Rabbis and Poskim and Elders of each community must be certain any fully aware of the following:
Therefore we should make every effort to obtain the ten individuals for services at the house of mourning, at a berit, etc. However, for the sake of sourcing and limud Tora lets look at so text for example an early Talmudic tradition indicated that even seven men were enough (Mas Soferim 10.6; Tos to Meg 23b).
This was based on a verse in Judges 5.2 which contains precisely seven words.
Our teachers in the West rule that seven [adult males are sufficient] and, as a reason for their ruling, they quote, When men let grow their hair in Israel, when the people offer themselves willingly, bless ye the Lord, [which implies that the number present must be the same] as that of the [Hebrew] words. Others hold that even six [adult males are sufficient for the purpose, since up to] bareku [the number of words] is six.
Furthermore, where there are nine or ten persons who have heard either bareku or ḳaddish and, after the service, one of them [who missed one of the benedictions] said bareku or ḳaddish, he has thereby performed [the duty of public worship].
The Sages long ago issued an ordinance to Synagogue precentors to say after the prayer for redemption, Blessed be the name of the Lord from this time forth and for ever, and after that, ‘Bless ye the Lord Who is to be blessed’, so as to enable those who had not heard the benedictions to perform the duty of public worship; for R. Joḥanan said: Would that a man read his prayers all the day long.
The congregations of the West and the congregations of the East have a custom to say it after ‘He Who maketh peace’ in the three statutory prayers of the Eighteen Benedictions, as a provision for the benefit of those who arrived late and for those who leave early. [The verse from Psalms with the benedictions is also said] even after the public reading from the Torah.
As regards the redemption of land, however, [the presence is required of] nine male adults and a kohen; and the same law applies to the redemption of a human being.
תני קטן וספר תורה עושין אותו סניף א"ר יודן כיני מתניתא קטן לספר תורה עושין אותו סניף
It was taught: They may count in a minor or a Torah scroll [with nine adults to reach the quorum of ten]. Said R. Yudan, “The correct version of the teaching is: They may count in a minor [with six adults to count as one of the seven who read from] the Torah scroll.”
Rabbi Michael Leo Samuel - Historic Precedent
On the other hand, there are other rabbinical passages dating back to the Gaonic era (8th-10th centuries) that in Palestine, a minyan may have consisted of seven or six people.
The liturgical historian Abraham Milgram notes that after WWII, a number of Jewish communities actually went back to counting six or seven people as a “minyan,” until the time their ranks would grow in number. This specifically happened in the city of Dubrovnik, Yugoslavia
Sourcing can be a very complex. If you have questions about these text please consult with a posek (expert in Jewish law) if you ever find the need to uses these or other sources.
As stated these sources are not to cause divisions in Yisrael but to beautify the teachings of our sages and to keep our faith alive in times of distress or great need.
Shabbat Shalom and Pesach Tov